1. Field of the Invention
The present invention relates to a backlight assembly for display devices and a liquid crystal display device having the same, and more particularly to a backlight assembly having an electromagnetic-wave shielding member for shielding an electromagnetic wave generated by a light source from an image display part of the liquid crystal display device and a liquid crystal display device having the same.
2. Description of the Related Art
Display devices have been developed together with information processing devices. The display device is an interfacing device between users and the information processing devices such that the users is able to identify the information processed by the information processing devices.
Among those display devices, a liquid crystal display (LCD) device is widely used since the LCD device can be manufactured to be lighter and thinner and can provide full-color and higher resolutions.
The LCD device displays information by using the optical properties of the liquid crystal molecules. Since the liquid crystal cannot emit a light by itself, the LCD device using the liquid crystal requires light so as to display an image. Accordingly, the LCD device usually employs additional light source. The LCD device usually displays an image using the light supplied from a backlight assembly. The backlight assembly is classified into a direct-illumination type and an edge-illumination type depending on the position of the light source such as a lamp. In the edge-illumination type backlight assembly, the lamp(s) is (are) disposed adjacent to at least one side face of a display panel for displaying an image, and the light exiting from the lamp is provided to the display panel through a light-guide plate. The light-guide plate changes the path of the light. The edge-illumination type backlight assembly has advantages of superior light uniformity, long endurance. The LCD device employing the edge-illumination type backlight assembly may have a thinner structure compared with the LCD device employing the direct-illumination type backlight assembly. For this reason, the edge-illumination type backlight assembly is usually installed in the LCD devices having a relatively small screen such as the LCD devices used in the laptop computers or desktop computers.
In the direct-illumination type backlight assembly, the lamp(s) is (are) disposed under the display panel, and the light exiting from the lamp does not pass through the light-guide plate and is directly incident into the display panel. That is, a plurality of the lamps parallel with one another is disposed under the display panel, and the light exiting from the lamps is irradiated onto an entire surface of the display panel, so that the direct-illumination type backlight assembly provides higher luminance compared with the edge-illumination type backlight assembly. For this reason, the direct-illumination type backlight assembly is usually installed in LCD devices having a relatively large screen.
However, the LCD devices have the following problems due to the backlight assembly.
The display panel usually includes a thin film transistor (TFT) substrate, a color filter substrate and a liquid crystal layer interposed between the TFT substrate and the color filter substrate. When an image signal is applied to the liquid crystal molecules, the arrangement of the liquid crystal molecules is changed, and the optical characteristics of the liquid crystal layer is changed. The liquid crystal display device displays the image using the changes of the transmissivity of the light passing through the liquid crystal layer.
The voltage level for driving the display panel is in a range from several volts to tens of volts since the voltage for driving the display panel is used only to change the arrangement of the liquid crystal molecules. However, the voltage level for driving the backlight assembly is in a range from several hundreds volts to several thousands volts since the voltage for driving the backlight assembly is used to turn on the lamp so as to generate the light. In particular, in case of the LCD device including the direct-illumination type backlight assembly, a plurality of lamps is simultaneously driven so that the voltage applied to the backlight assembly is hundreds or thousands times higher than the voltage applied to the display panel.
Since the intensity of an electric field is proportional to the voltage, the intensity of the electric field applied to the backlight assembly is hundred or thousands times higher than the intensity of the electric field applied to the display panel. Therefore, the electrical characteristics of the display panel into which the image signal is applied may be affected by the electromagnetic waves due to the high voltage signal applied to the lamp(s). When the image signal is disturbed, the correct image may not be displayed on the display panel. The electromagnetic waves may be generated by the electric field caused by the voltage applied to the lamp and by other electromagnetic changes during the discharge of the lamp. The electromagnetic waves due to the high voltage signal applied to the lamp cause electromagnetic disturbance in the liquid crystal display panel and change the electromagnetic characteristics of the display panel, so that the display failure may occur. Accordingly, the display quality of the LCD device may be deteriorated by the electromagnetic disturbance. In particular, the display quality debase is remarkably observed in the LCD device including the direct-illumination type backlight assembly since a plurality of lamps is disposed under the display panel.